1. Field of the Invention
The invention relates to a method and apparatus for zone-annealing of the generic type.
2. Description of the Prior Art
It is known that workpieces consisting of high-temperature materials, especially of dispersion-hardened high-temperature alloys, such as nickel-based superalloys, have to undergo coarse-grain annealing at the end of their production process. This heat treatment is necessary in order, in particular, to achieve good mechanical properties (high creep resistance) at high operating temperatures and to obtain grains which are elongated in the direction of tensile stress and which have increased strength and ductility. This can be accomplished by means of so-called zone-annealing if a temperature gradient in the appropriate direction is employed (see U.S. Pat. No. 221,979 of July 31, 1972, now abandoned, and No. DE-B-2,303,802).
The problem arising in all existing zone-annealing plants is that, particularly when the geometry of the workpiece is complicated, it is only rarely possible to force the temperature gradient to follow the desired longitudinal direction in an ideal manner. There is therefore the need to seek new methods and processes associated with them.